Chitosan for the coagulation and flocculation of mineral colloids

Chitosan dissolved in acetic or hydrochloric acid was used for the coagulation and the flocculation of bentonite colloids. The influence of pH was investigated and the double effect of the biopolymer was identified. Experiments were performed at different polymer concentrations and at different pHs with simulated suspension (prepared with different amounts of bentonite). At pH 5 (acidic region), the protonation of amine groups led to coagulation effect and very low amounts of polymer were required to achieve a fast and efficient decantation of colloids; at pH close to neutral, a different mechanism was involved in the flocculating effect of the polymer chain (larger amounts of polymer were usually required). The effect of the characteristics of the polymer, i.e., degree of deacetylation, and polymer weight (related to polymer viscosity) was also investigated in order to optimize the selection of the biopolymer for targeted experimental concentrations.